During the manufacture and fabrication of steel beams and the like, the steel beam must be accurately positioned to be cut, punched, drilled, sheared, or even welded. These steel beams vary from four inches to forty inches wide and can be up to sixty-five feet long. In addition, the steel may be hot where it is being cut at the steel mill. One prior art system which has been used to measure the linear displacement of a steel beam includes a pinch roller. The pinch roller is pressed against the beam and an electronic encoder on the pinch roller counts the distance that the beam moves. However, as the wear on the roller constantly reduces the diameter of the roller, this diameter must be checked every day and the wear compensated for. U.S. Pat. No. 3,556,368 discloses a measuring system of this type having conveying and measuring pinch rollers located on either side of a work station. Another more common system uses a rack and gear. However, this system also must be compensated for wear. Also, when this system is used on a conveyor, material cannot be taken off the side of the conveyer that the measuring system is located on.
A number of measuring systems have also been disclosed in the prior art for measuring lengths of linear material. For example, in U.S. Pat. No. 3,758,954 to Teplitz, a measuring apparatus for bridge wire strands is disclosed. This apparatus includes a calibrated tape traveling around a plurality of pulleys and in contact with the wire strand along a portion of the travel. A separately mounted chain with magnets located inside of the tape is used to clamp a portion of the tape to the wire strand as it passes by. Another linear position measuring device is disclosed in U.S. Pat. No. 4,068,384 to Holly et al. This device is designed for use with a conveyor and includes a magnetic strip which is bonded to a side of the conveyor. A steel belt travels between two pulleys and a portion of the steel belt is held magnetically to the magnetic strip. A measuring device on one pulley is then used to measure the movement of the steel belt and thus the movement of the conveyor. A linear measuring system for precisely measuring distances along a rather long measurement axis is disclosed in U.S. Pat. No. 4,091,541 to DiCiaccio. In this system, the object is attached to a mechanical coupler. An endless measuring cable is attached to one side of the coupler and travels around an idler drum and a measuring drum and back to the other side of the coupler. As the object moves, a rotary encoder produces a digital output signal in response to the movement of the measuring drum. Still another measuring system for measuring the length of a web, such as a floor covering or the like, is disclosed in U.S. Pat. No. 4,195,410 to Strohmeyer. This device uses a measuring roller which is directly coupled to a measuring mechanism. While the devices disclosed above may be suitable for the particular environment in which they are found, these devices are not suitable for measuring variable sized steel beams and the like.